How do I delete wireless networks from my iPhone?

You can get rid of those by Resetting Network Settings from Settings > General > Reset.

Reset network settings

Go to Settings > General > Reset and tap Reset Network Settings.

When you reset network settings, your list of previously used networks and VPN settings not installed by a configuration profile are removed. Wi-Fi is turned off and then back on, disconnecting you from any network you’re on. The Wi-Fi and “Ask to Join Networks” settings remain turned on.

To remove VPN settings installed by a configuration profile, go to Settings > General > Profile, then select the profile and tap Remove. This also removes other settings or accounts provided by the profile.

(From http://manuals.info.apple.com/en_US/iphone_user_guide.pdf)

You have to reset all network settings.

Settings > General > Reset > Reset Network Settings.

As far as I know, you cannot pick and choose which networks to reset. This will require you to re-enter any network passwords, so make sure you have the password ready for the network you are using now.

EDIT: Nevermind.... forgot about "forget this nework!"

Message was edited by: Iynque

Settings --> WiFi --> Tap the network name and then tap the Forget This Network button

You will have to tap the blue arrow on the right side, actually.

You can only "forget" networks when you are actually connected to the network.

You have to be in range of the network so that it shows in the list, but you do now have to be connected to it.

You mean you reset all network settings and it doesn't ask for new credentials when you join the network again?